When you don't get enough iron or protein -- or you get too much vitamin A -- your hair can fall out. Get protein from meat, eggs, and beans. Get iron from fortified cereal, spinach, and clams. You can use supplements, but it's better to get your vitamin A from food so you don't overdo it.
Some people notice hair loss when they lose more than 15 pounds. The hair loss usually starts about 3 to 6 months later, but the hair will grow back on its own.